1. Field of the Invention
The present invention relates to a display device, and more particularly, to a display device with an integrated touch screen.
2. Discussion of the Related Art
A touch screen is an input device included in image display devices such as Liquid Crystal Displays (LCDs), Field Emission Displays (FEDs), Plasma Display Panel (PDPs), Electroluminescent Displays (ELDs), and Electrophoretic Display (EPDs). Thus, the user can input information by applying a pressure (e.g., a pressing or touching) to a touch sensor of the touch screen while viewing the image display device. Further, the demand for display devices with an integrated in-cell type touch screen such as smart phones and tablet Personal Computers (PCs) is increasing.
Hereinafter, a related art display device with an integrated touch screen will be described with reference to FIG. 1. In more detail, FIG. 1 is a diagram illustrating a related art display device with an integrated touch screen, and particularly illustrates a display device with an integrated self-capacitive touch screen having an in-cell type.
As shown, the related art display device includes a panel 10 that includes two groups 11; a display driver IC (DD-IC) 20 connected to an external system and which controls gate lines and data lines in the panel 10; and touch ICs (T-IC1 and T-IC2) 30a and 30b which drive the two groups 11. Further, each of the two groups 11 includes electrodes 12 and lines 13 respectively extended from the electrodes 12. Each of the touch ICs 30a and 30b includes touch IC channels respectively corresponding to the lines 13 for self-capacitive touch sensing.
In addition, each of the electrodes 12 is built in the panel 10 and performs a touch function and a display function, and thus functions as a common electrode for display driving when the display device is driven in a display driving mode, or as a touch electrode when the display device is driven in a touch driving mode.
Voltages and signals applied by groups according to a driving mode will now be described in detail with reference to FIGS. 1 and 2. When a driving mode of the panel 10 is the display driving mode, a common voltage is applied to the electrodes 12 through the touch ICs 30a and 30b. Thus, the electrodes 12 receive the common voltage and are thereby used as common electrodes for display driving.
When the driving mode of the panel 10 is the touch driving mode, a touch scan signal for touch sensing is applied from the first touch IC 30a to the first group 11a, and a ground-level voltage or a floating voltage is applied from the second touch IC 30b to the second group 11b. Here, the electrodes included in the first group 11a are used as touch electrodes for touch sensing. Then, the touch scan signal for touch sensing is applied from the second touch IC 30b to the second group 11b, and the ground-level voltage or the floating voltage is applied from the first touch IC 30a to the first group 11a. Similarly, the electrodes included in the second group 11b are used as touch electrodes for touch sensing.
On the other hand, assuming a common voltage of about −2V is applied to the electrodes of a group for display driving in the display driving mode, and the ground-level voltage of 0V or the floating voltage is applied to electrodes of a group to which the touch scan signal is not applied in the touch driving mode, there is a drop of a voltage applied to a pixel electrode in the display driving mode and the touch driving mode. Thus, a block dim occurs due to the difference between voltages applied to electrodes of a group.
When the voltage drop is continued for a certain time or more, the liquid crystal is twisted, and thus the grayscale level of the liquid crystal is shifted, causing a flicker phenomenon. Also, in the touch driving mode, because a display driving voltage is not shifted identically to the display driving mode, a voltage formed in a pixel is asymmetrically formed with respect to the ground-level voltage of 0V.
To summarize, the related art display device with an integrated touch screen has the following problems. First, in the display driving mode and the touch driving mode, a block dim occurs in a pixel electrode due to a difference between voltages applied to electrodes of a group. Second, the grayscale level of liquid crystal is shifted due to the drop of a driving voltage, causing flickers. Third, a positive voltage and a negative voltage are asymmetrically formed with respect to the ground-level voltage in a pixel, and thus flickers increase.